The Sound Transmission Class (STC) is a recognized standard and is the most common sound isolation standard in use in North America today. The STC is a method established in 1961 for rating the “noise reduction” capabilities of walls over the frequency range of 125-4000 assuming that the noise the wall is trying to stop is generally even across the frequency spectrum. The rating is calculated by using a “contour” that is shifted up and down to the highest point were two conditions are satisfied. To calculate STC, one has to attain performance data, which is called transmission loss, from a certified laboratory. Once the transmission loss (TL) data is attained, STC can be calculated.
Some commonly accepted STC ratings for wall constructions are illustrated in the following TABLE 1:
TABLE 1DescriptionEstimated STC RatingWall Assembly3⅝″ metal studs, ⅝″ gyp (2 layers total), No insulation38-40 3⅝″ metal studs, ⅝″ gyp (2 layers total), Batt insulation43-44 2 × 4 stud, ⅝″ gyp (2 layers total), Batt insulation34-39 Staggered studs, ⅝″ gyp (2 layers total), Batt insulation46-47 2 × 4 stud, ⅝″ gyp (2 layers total), Resilient Channel, Batt insulation45-52 3⅝″ metal studs,  ⅝″ gyp (3 layers total), Batt insulation39-40 2 × 4 stud, ⅝″ gyp (4 layers total), Batt insulation43-45 2 × 4 studs, ⅝″ gyp (4 layers total), Batt insulation44-45 2 × 4 studs, ⅝″ gyp (2 layers total), Batt insulation56-59 2 × 4 studs, ⅝″ gyp (3 layers total), Batt insulation59-60 2 × 4 studs, ⅝″ gyp (4 layers total), Batt insulation58-63
Typical interior walls in newer home constructions, using 2 sheets of ½″ drywall on either side of a wood stud frame, have an STC of about 33. When asked to rate the acoustical performance of these walls, people often describe them as being “paper thin.” Accordingly, such wall constructions offer little in the way of sound-dampening or privacy.
Adding absorptive insulation (e.g., fiberglass batts) in the wall cavity usually increases the STC of typical walls to fall within the range of 36-39, depending on stud and screw spacing. Doubling up the drywall in addition to insulation can yield an STC rating in the range of about 41-45, provided the wall gaps and penetrations are sealed properly.
It is important to note that doubling the mass of a partition does not double the STC rating. Doubling the mass (e.g., going from two total sheets of drywall to four) typically adds only about 5-6 points to the STC rating. Breaking the vibration paths by decoupling the panels from each other will increase transmission loss much more effectively than simply adding more and more mass to a monolithic wall/floor/ceiling assembly.
Structurally decoupling the drywall panels from each other (by using resilient channel, steel studs, a staggered-stud wall, or a double stud wall) can yield an STC rating as high as 63 or more for a double stud wall, with good low-frequency transmission loss as well. Compared to the baseline wall of STC 33, an STC 63 wall will transmit only about 1/1000 as much sound energy, seem about 88 percent quieter and will render most frequencies inaudible. However, such wall assemblies can add a significant cost to the overall construction price.
Due to their high mass, concrete and concrete block walls have good TL values (STC ratings in the 40s and 50s for 4-8″ thickness) but their weight, added complexity of construction and poor thermal insulation tend to limit them as viable materials in most residential wall construction, except in temperate climates and hurricane or tornado prone areas. Various insulation options can result in higher STC ratings, however, insulation tends to add little compared to other aspects of wall construction.
Materials which can improve the STC rating in walls include mass-loaded vinyl (MLV), standard drywall, “soundproof” drywall, such as QuietRock™, Supress™, SoundBreak™ and ComfortGuard™ or damping compounds such as Green Glue™. However, each of these products have drawbacks such as cost, complexity of application or construction, as well as other problems. The present material and disclosed methods solve these and other issues found in prior art sound-dampening.